Page:Final Report - The Columbia River Interstate Bridge.pdf/33



The foundation piles are cut off a few feet below low water so that the upper ends of these piles are imbedded into the concrete of the bases of the piers from 15 to 20 ft. and the piles form a definite portion of the pier. It is evident that even though some unusual scour should, on some extraordinary occasion, extend below the bottom of the base, the pier would still be perfectly stable, owing to the great depth of penetration of the piles and to the rigidity of their upper support. Around each pier base there is an amount of heavy stone rip-rapping, which should be replenished, if necessary, during the next few years.

The shafts of the piers above the base are comprised of two cylindrical battered columns, one placed under each pair of shoes. These columns are joined by a vertical diaphragm and by the horizontal coping at the top, both of which are reinforced with steel. This design saves considerable weight which otherwise would require supporting piles and eliminates a large amount of concrete unnecessary for any structural purpose.

The occurrence of ice in the Columbia River in sheets or ﬂoes of large size is very rare, so that the concrete piers need no special protection of steel or stone facing.

The bridges over the sloughs consist of deck spans providing a roadway and ﬂoor of the same type and character as previously described, except that the girders are placed 23 ft. apart